Conventionally, exclusive control of access to the same resource by a plurality of CPUs is executed by an OS (Operating System) or a scheme for preparing a semaphore flag in a memory area which can be accessed commonly by the respective CPUs, and accessing a bus after confirming the flag (see Japanese Patent Laid-Open No. 5-20279).
In the former prior art, all exclusive control processes are left to the OS, putting a load on software. The latter prior art, i.e., the method of preparing a flag in a memory area suffers generation of a time lag in memory access, or a failure in an exclusive process upon simultaneous access to the flag in the memory area.